|As Chuck2 alluded to, you can't install XP on a HDD in one system, then swap it in another...it doesn't work that way. You either have to do a clean install in the system it's gonna be used in, or do an "over the top" installation (aka "repair installation") in the system you swapped the drive into.|
It's very likely that nothing was wrong with the hardware until you started mucking around inside the case. You obviously knocked something loose or installed something improperly.
As for the beep codes, it's depends on which BIOS your motherboard uses. My guess is you have an AMI BIOS:
1 long, 8 short = The video adapter is either missing or defective.
2 short = Memory parity error or POST Failure.
1 short = DRAM refresh failure.
Sounds like the problem is memory related.